Poly(vinylidene fluoride) membranes have been widely applied in many areas including low pressure water treatments, microfiltration, ultrafiltration, nanofiltration and distillation, thanks to the outstanding chemical, thermal and mechanical stability of poly(vinylidene fluoride).
Nevertheless, poly(vinylidene fluoride) membranes may suffer certain disadvantages in these applications because of their hydrophobic nature and thus their poor wettability.
Especially when treating aqueous solutions containing suspended solids, because of the low surface energy of PVDF, these materials tend to be adsorbed onto the surface and into the pores of the PVDF membrane, thus causing fouling. The extent of adsorption is generally believed to depend on the foulant-membrane interactions such as hydrophilic/hydrophobic interactions, hydrogen bonding, van der Waals interactions and electrostatic effects.
While some specific operational procedures may be applied in order to reduce fouling (turbulent conditions, for instance with air bubbles flux, periodic backwash, treatment with chemical cleaning agents), these mitigating actions make operations more complex and economically burdensome and may, especially in the case of chemical cleaning, have negative effects on the durability of membrane materials.
Approaches have been thus developed for preventing fouling mechanism by modifying the membrane material itself, for increasing its hydrophilicity, e.g. by surface coating, surface grafting or blending.
For instance, WO 2008/129041 (SOLVAY SOLEXIS S.P.A.) 30 Oct. 2008 discloses linear semi-crystalline copolymers of vinylidene fluoride comprising from 0.05% to 10% by moles of recurring units derived from hydrophilic (meth)acrylic monomers, said copolymers having a random distribution of the recurring units derived from said (meth)acrylic monomers throughout the whole vinylidene fluoride backbone, said copolymers being notably suitable for the manufacture of hydrophilic membranes.
Also, MENG, Fangang, et al. Recent advances in membrane bioreactors (MBRs): membrane fouling and membrane material. Water Research. 2009, vol. 43, p. 1489-1512. discloses PVDF ultrafiltration membranes coated with polyvinyilidene fluoride-graft-polyoxyethylene methacrylate copolymer.
Further, LIU, Fu, et al. Preparation of hydrophilic and fouling resistant poly(vinylidene fluoride) hollow fiber membranes. Journal of Membrane Science. 2009, vol. 345, p. 331-339. discloses PVDF hollow fiber membranes blended with random copolymer of methyl methacrylate with poly(ethylene glycol)methyl ether methacrylate.
There is nevertheless still a current shortfall in the art for alternative vinylidene fluoride polymers exhibiting outstanding hydrophilic surface properties, while maintaining the other outstanding properties of the vinylidene fluoride polymers, e.g. thermal stability and mechanical properties, and which can be manufactured in an easy manner, without involvement of subsequent grafting or blending or otherwise chemical modification. Similarly, there is a need in the art for innovative manufacturing process enabling preparation of such materials.